A major question in multiple sclerosis research is the mechanism responsible for the development of neurologic deficits following demyelination. The goal of this proposal is to test the hypothesis that effector molecules released by CD8+ T cells cause neurologic deficits following demyelination by destroying or disrupting the function of axons and neurons. We have used the Theiler's virus model of demyelination to dissect the components of the MHC-restricted class I (CD8 T cells) versus MHC-restricted class II (CD4 T cells) responses to neurologic dysfunction following demyelination. Infection of class I- deficient mice results in prominent demyelination in the absence of neurologic deficits, whereas infection of class 11-deficient mice of identical genotype results in demyelination with severe neurologic dysfunction. Our first specific aim is to determine the effector molecules produced by cytotoxic T cells (IFN-gamma, Fas, TNF, and perforin) critical for induction of neurologic deficits by examining neurologic function and electrophysiology in immune knockout mice (IFN- gamma-/-, IFN-gammaR -/-, TNF -/-, TNFR -/-, PFP -/-, Fas -/-, FasL -/- )in mice of genotype resistant or susceptible to demyelination. We will also do adoptive transfer experiments into immunodeficient RAG -/- mice to determine the contribution of effector molecules with CD8 and CD4 cells to demyelination and neurologic deficit. Our specific second aim is to define the morphologic basis for functional deficits by determining whether axons are destroyed or injured in mice with immune effector deficiency following virus infection. We will assess degree of axonal dropout in normal and demyelinated white matter, perform neurofilament staining by immunofluorescence, count neurons in nuclei by retrograde labeling, and assess sodium channel distribution by [H3] saxitoxin autoradiography and fluorescence immunocytochemistry. These experiments are expected to provide new insights into the effector molecules released by the inflammatory response responsible for neurologic deficits in demyelinating disease.